"There will be substantial industrial action but the dates will change," Unite's spokesperson told Reuters.
Responding to a Reuters request for comment, Heathrow Airport said it has not yet received any formal notice from Unite on their intention to strike.
In an earlier release, Unite had specified that the strike would be for 33 days, kicking off on June 17.
Unite General Secretary Sharon Graham has said: “Escalating strike action will inevitably cause disruption, delays and cancellations across Heathrow.”
TM/PR